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161.
S. Majid Hassanizadeh 《Transport in Porous Media》1996,23(1):107-124
The Fickian dispersion equation is the basic relationship used to describe the nonconvective mass flux of a solute in a porous medium. This equation prescribes a linear relationship between the dispersive mass flux and the concentration gradient. An important characteristic of the Fickian relationship is that it is independent of the history of dispersion (e.g. the time rate of change of the dispersion flux). Also, the dispersivities are supposed to be medium constants and invariant with temporal and spatial scales of observation. It is believed that in general these restrictions do not hold. A number of authors have proposed various alternative relationships. For example, differential equations have been employed that prescribe a relationship between the dispersion flux and its time and space derivatives. Also, stochastic theories result in integro-differential equations in which dispersion tensor grow asymptotically with time or distance. In this work, three different approaches, which lead to three different non-Fickian equations with a transient character, are discussed and their primary features and differences are highlighted. It is shown that an effective dispersion tensor defined in the framework of the transient non-Fickian theory, grows asymptotically with time and distance; a result which also follows from stochastic theories. Next, principles of continuum mechanics are employed to provide a solid theoretical basis for the non-Fickian transient dispersion theory. The equation of motion of a solute in a porous medium is used to provide a rigorous derivation of various dispersion relationships valid under different conditions. Under various simplifying assumptions, the generalized theory is found to agree with the conventional Fickian theory as well as several other non-Fickian relationships found in the literature. Moreover, it is shown that for nonconservative solutes, the traditional dispersion tensor is affected by the rate of mass exchange of the solute.Also with National Institute of Public Health and Environmental Protection (RIVM), PO Box 1; 3720BA Bilthoven, The Netherlands 相似文献
162.
DFT calculations are employed to compare and contrast six-membered ring carbenes including 1,3-dimethyltetrahydropyrimidin-2-ylidene (1a), 1-methyl-3-cyclopropyltetrahydropyridine-2-ylidene (2a), and 1,3-dicyclopropylcyclohexane-2-ylidene (3a) as well as their unsaturated analogues 1b, 2b, 3b, and 2c. The amino groups exert singlet-triplet energy separation (?Es−t) of 60.9 kcal/mol to 1a while cyclopropyls induce a ?Es−t of 14.8 kcal/mol to 3a. The simultaneous presence of amino and cyclopropyl in 2a leads to a ?Es−t of 43.3 kcal/mol. Unsaturation slightly increases the ?Es−t of 1a and 3a but not that of 2a. Our thermodynamic, kinetic, and reactivity results are compared with those of synthetic five-membered ring N-heterocyclic carbenes. 相似文献
163.
Due to the opposite surface charge of TiO(2) and silver nano-particles, at around neutral pH, it is expected that the interaction between these particles and cross-linkable polysiloxane (XPs) resin and thus their final properties would be affected by their processing technique. This paper has focused on the effect of processing design on the interaction, surface orientation and final properties of surface nano-colloidal functionalization. The results disclosed the key role of the applied process on the properties of the treated fabrics which have been well discussed through the modeling of this effect on orientations of nanoparticles on the surface. The developed models are interestingly verified by various characterizations. Applying a premixed TiO(2)/XPs colloid as an after treatment on Ag treated samples caused more enhanced stain photo-degradability and UV protection properties, while the reduction of enhanced hydrophobicity, washing durability, and stain-repellency were observed as compared to applying Ag/XPs premixed colloid on TiO(2). The role of processing on XPs stabilizing efficiency and its co-photo-catalytic function on TiO(2) nanoparticles has been concluded and deeply discussed. The appropriate processing design can be tailored in order to accomplish desirable hydrophilicity/hydrophobicity with a granted bioactivity. The results reveal that ideal bioactivity, stain photo-degradability, self-cleaning, UV protection, anti-staining properties, and washing durability can be achieved by applying a mixture of silver and XPs as an after-treatment on TiO(2) treated fabrics. 相似文献
164.
This paper focus on the effect of nanosize (<50 nm BET) inorganic alumina (Al2O3) filler on the structural, conductivity, and thermal properties of chitosan‐based polymer electrolytes. Films of chitosan and its complexes were prepared using solution‐casting technique. Different amounts of Al2O3 viz., 3, 4.5, 6, 7.5, 9, 12, and 15 wt% were added to the highest room temperature conducting sample in the chitosan–salt system, i.e. sample containing 60 wt% chitosan–40 wt% NH4SCN. The conductivity value of the sample is 1.29 × 10?4 S cm?1. On addition of 6 wt% Al2O3 filler the ionic conductivity increased to 5.86 × 10?4 S cm?1. The amide and amino peaks in the spectrum of chitosan at 1636 and 1551 cm?1, respectively, shift to lower wavenumbers on addition of salt. The glass transition temperature Tg for the highest conducting composite is 190°C. The increase in Tg with increase in more than 6 wt% filler content is attributed to the increase in degree of crystallinity as proven from X‐ray diffraction studies. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
165.
Zahra Shariatinia Mauricio F. Erben Carlos O. Della Védova Majid Abdous Saman Azodi 《Structural chemistry》2011,22(6):1347-1352
Intermolecular interactions between α-, β-glucose, and methacrylic acid (MAA) have been investigated. Twenty-two possible
conformations have been optimized at the DFT(B3LYP) level of theory with the 6-31G(d) basis set. The geometrical parameters
for the most stable configurations of hydrogen bonding sites in the optimized systems have been determined. The binding energies
ΔE
bind have been calculated at the MP2/6-311++G(d,p) level of approximation taking into account the basis set superposition error
(BSSE) and the zero-point vibrational energies corrections. Results indicate that the most stabilized complexes form hydrogen
bonds either through carboxylic and hemiacetal oxygen atoms acting as proton acceptors. Both, α- and β-anomers are studied
in the pyranose six-membered ring. In all complexes, the nuclear quadrupole coupling constants (χ) for 17O nuclei were obtained about 10.0 MHz, while for the 2H atoms they vary from ≈200.0 to ≈350.0 kHz. 相似文献
166.
Mahboubeh Rostami Ahmad R. Khosropour Valiollah Mirkhani Iraj Mohammadpoor-Baltork Majid Moghadam Shahram Tangestaninejad 《Comptes Rendus Chimie》2011,14(10):869-877
Di[1,6-bis(3-methylimidazolium-1-yl)hexane] decatungstate dihydrate ([C6(MIm)2]2W10O32. 2H2O) as a new family of polyoxometalate-based dicationic ionic liquids (POM-DIL) is synthesized and employed as a novel and powerful heterogeneous catalyst in the synthesis of 4-arylidene-2-phenyl-5(4)-oxazolones (azlactones) under ultrasound-assisted solvent-free condition. On the basis of the results, the products were obtained in excellent yields under mild condition. Utilization of easy work-up and purification make it very interesting from an economic perspective. Moreover, a recycling study confirmed that the catalyst can be reused multiple times without significant loss of its activity. 相似文献
167.
Shabi Abbas Zaidi Seung Mi Lee Zeid A. AL Othman Abdullah M. AL Majid Won Jo Cheong 《Chromatographia》2011,73(5-6):517-525
Some acidic chiral templates were used to prepare open tubular (OT) molecule imprinted polymer (MIP) capillary columns to explore the effects of molecular structures of templates on chiral recognition capabilities and to verify the feasibility of the general MIP preparation protocol introduced in the previous study. The templates are phenyl carboxylic acids and their derivatives. Optimization was carried out for chiral separation of template enantiomers for each MIP column through varying pH and composition of eluent. It was found that the preparation protocol can be successfully applied for the appropriate templates with functional groups fulfilling the three-points interaction rule. The chiral separation performances were quite satisfactory for MIPs of such templates although they are yet inferior to the separation performances of the MIP columns fabricated with the templates of profen drugs (2-arylpropionic acids with a large substituent on the phenyl ring). Subtle variations of the template molecular structures have been found to be critical to enhance chiral recognition ability of the resultant MIP column. 相似文献
168.
Iraj Mohammadpoor‐Baltork Majid Moghadam Shahram Tangestaninejad Valiollah Mirkhani Zohre Eskandari 《Journal of heterocyclic chemistry》2011,48(2):479-483
An efficient method for the selective synthesis of 2‐substituted oxazines and tetrahydropyrimidines by the reaction of arylnitriles with 3‐amino‐1‐propanol and 1,3‐diaminopropane in the presence of montmorillonite K‐10 and KSF as inexpensive, environmentally benign, and reusable catalysts under classical heating conditions and microwave irradiation is reported. J. Heterocyclic Chem., (2011). 相似文献
169.
Abbas Afkhami Tayyebeh Madrakian Saeid Soltanbeygi Majid Rezaeivala 《Journal of Molecular Structure》2011,985(1):86-90
The complex formation between a new synthesized Schiff base and the cations Ni2+, Co2+, Cu2+, Zn2+ in dichloromethane (DCM) and chloroform solutions was investigated spectrophotometrically using rank annihilation factor analysis (RAFA). The results of mole ratio plots and continuous variation data show the stoichiometry of complexation were found to be 1:1, and 2:1 metal ion to ligand. The stoichiometry was obtained as 1:1 metal ion to ligand ratio for Co2+, Ni2+ and Zn2+ in chloroform and 2:1 for Cu2+. In DCM the stoichiometry was obtained as 1:1 for Co2+ and 2:1 for Ni2+ and Zn2+ and a consecutive 2:1 metal ion to ligand ratio was obtained for Cu2+. Formation constants of these complexes were estimated by application of RAFA on spectrophotometric data. In this process the contribution of ligand was removed from the absorbance data matrix when the complex stability constant acts as an optimizing object and simply combined with the pure spectrum of the ligand, the rank of the original data matrix can be reduced by one by annihilating the information of the ligand from the original data matrix. 相似文献
170.
Majid Montazer Esfandiar PakdelAuthor vitae 《Journal of Photochemistry and Photobiology, C: Photochemistry Reviews》2011,12(4):293-303
The consumption of titanium dioxide in today's world is on the increase. As the most popular nano substance, TiO2 is used in various industries notably in the textile industry. More and more recently, through a synergistic combination of photocatalytic features of nanoparticles, fabrics with novel properties are produced. Self-cleaning and stability against UV rays as well as chemical media, to name but a few, are among new prominent properties, obtained on textiles. A common subject reported in most studies has been the diverse approaches to immobilize the nanoparticles on the surface of fabrics. Wool is among common textile materials that have undergone numerous processes to be modified. This review intends to bring to light different aspects of application of nano titanium dioxide in the textile industry especially on wool, and also presents a concise overview on the rigorous pieces of research conducted in this realm. 相似文献